International application WO 2009/158105 relates to an imaging module made up of a number of transparent substrates, which substrates are on either side provided with so-called aperture layers, a number of lens elements, wherein said lens is disposed on either side of the aforesaid substrate, such that said aperture layer is embedded between said lens and said substrate, and an image sensor of the pixel array type.
European application No. 2 202 796 in the name of the present applicant relates to an optical unit, comprising, seen in a direction from the object side to the imaging surface, a first substrate, a first lens element, a flat, transparent intermediate layer, a second lens element and a second substrate, which intermediate layer has an optical correction function near the imaging surface.
International application WO 2010/074743 relates to a method for forming an imaging module, wherein a lens stack wafer, a spacer wafer and an image sensor wafer are formed into a module.
US 2010/0118420 relates to an image capture lens comprising a first glass substrate, a first lens material on one side of said substrate and a second lens material on the other side of the substrate.
Optical units are known per se, they are used, inter alia, in camera systems, in relation to which systems an ongoing effort exists to find smaller, lighter, thinner, better and cheaper camera systems. From International application WO 2004/027880 in the name of the present applicant, for example, there is known a camera system comprising an image capturing element, a lens element for imaging an object at the image capturing element, a spacer for maintaining a predetermined distance between the lens element and the image capturing element, whilst furthermore a tens substrate is provided for carrying the lens. From U.S. Pat. No. 6,985,307 there is furthermore known a lens assembly wherein it is indicated that the optical length, which is defined as the distance between the object side of the imaging lens to the imaging surface of a CCD or the like, must be small. Such a lens is frequently also referred to as a compact lens, wherein, for example in a mobile phone, the optical length must be at least less than the thickness of the telephone itself. The lens must furthermore be configured so that the image obtained with such a lens be visually acceptable. U.S. Pat. No. 6,985,307 thus provides a lens assembly made up of a first lens element, a second lens element and a third lens element, which lens elements must meet special requirements as regards their curvature, the relative spacing between the lens elements and the thickness of the lens elements used. From International application WO 2008/011003 there is furthermore known a camera system comprising three substrate layers with five optical elements formed thereon.
The camera modules used in mobile telephones require increasingly more resolution and optical functionalities within ever decreasing dimensions. Thus, there is a need for the development of new lens systems comprising lens elements having a greater sag height, sometimes referred to as deeper lenses elements, which lens elements must have at least the same dimensional precision as the prior lens elements. The present applicant has found that, using the current production methods, significant efforts are required in order to control the intended dimensional precision with the increasingly deep lens elements.